Long term performance of low voltage aerial bundled cable

The objective of this research is to identify and evaluate factors which may influence the long-term performance of the low voltage aerial bundled cable system erected within the boundaries of the South East Queensland Electricity Board's area of supply. Field inspections of a number of in-service installations were carried out which identified a range of problems relating to the corrosion of bolts and ABC conductor cores when erected in close proximity to surf beaches. The scope of the project was restricted to an investigation related to the ABC system's resistance to corrosion, its limits of electrical and mechanical performance, and the degradation of materials due to exposure to ultraviolet radiation. Abrasion and vibration in the ABC system was not envisaged to be a major factor in limiting the long-term performance of the system. The course of the research identified the major mechanism by which moisture and pollutants are permitted to enter conductor cores at insulation piercing connector sites. The testing program showed that insulation piercing connectors were unable to prevent the ventilation of air in the interstices within the stranded conductor core under the action of air pressure differentials being caused by increases and decreases of cable temperature. The research also showed that the XLPE insulation of the conductors can be damaged when the system is subjected to certain overload and short circuit conditions. A methodology has been developed which can define the mechanical limits of the XLPE insulation by the use of "kneeing curves". This allows a process to be used which will enable an appropriate size of low voltage fuse to be selected for protection of the insulation under overload and short circuit conditions. Photomicrographs of samples of XLPE insulation recovered from inservice applications show that some cable insulation has been manufactured with poor carbon black dispersion, but the degrading effects of ultraviolet radiation have not been determined. A number of conclusions and recommendations can be made as a result of this research which have the potential to significantly improve the long term performance of low voltage aerial bundled cable